Changes in dewatering properties between the thermophilic and mesophilic stages in temperature-phased anaerobic digestion systems

Temperature-phased anaerobic digestion (TPAD) has become increasingly appea ling in recent years because of the pathogen destruction capabilities of th e system. However, there has also been concern about the dewatering propert ies of the solids created by these systems. A laboratory study was conducte d at Virginia Polytechnic Institute and State University, Blacksburg, to de termine the effect of thermophilic solids retention time (SRT) on dewaterin g properties of wastewater solids to characterize system parameters associa ted with dewatering and to understand the mechanisms causing changes in dew atering properties between the thermophilic and mesophilic phases. The stud y showed that, while anaerobic digestion caused dewatering properties to de teriorate, the solids varied little with thermophilic SRT. Acidogenesis was essentially complete after 1.5 days. Subsequent mesophilic digestion resul ted in little change to dewatering properties and modest reductions in cond itioning doses, but substantial reductions in biopolymer (protein and polys accharides) occurred. It seems that thermophilic anaerobic digestion create s or releases colloidal materials that cause dewatering to be poor and subs equent mesophilic digestion for 15 days does little to improve the dewateri ng properties of solids in TPAD systems.